Originally Posted by mmdavidson0128
I have no...absolutely zero doubt that this happened...But I believe without a shadow of doubt that there was was one or more factors that caused such a catastrophe. I car doesn't nearly go up in flames because the battery when dead and it was to taxing for the charging system to recharge the battery. I'm not a mechanic by any stretch for sure but respectfully that wreaks highly of some other issue present before the battery died.
Actually it's pretty easy to understand how it can cause a fire.
Again this depends on the amperage capacity of the alternator but the problem isn't the act of charging the battery with the alternator. The problem is when an anemic alternator is over taxed by trying to charge a flat battery for an extended period of time, causing it to heat up beyond what it was designed to do. That's not to say that it *ALWAYS* causes your alternator to go boom though. The odds are you're going to shorten the life of your alternator if you ask it to charge a dead battery though.
What usually goes boom inside the alternator is the full bridge rectifier, which is nothing more than a series of diodes. It's those diodes that can't take the heat and when they fail, "bad things" start to happen.
Batteries don't like AC current being directly applied to them. The diodes in your alternator act like one way valves and take the AC sine wave that the alternator generates and smooths it out to a nice flat DC voltage that your car and battery can use.
When the diodes fail instead of that nice smooth DC voltage being created, you start getting either a half or full sine wave being output from the alternator. That's when bad things start to happen. Bad things like your vehicle's ECU resetting itself while your driving, the brushes on DC motors (like the ones in your cooling fans) get fried, if the sine wave happens to be negative biased it starts to wreck electrolytic capacitors (caps REALLLY HATE having reverse voltage applied to them. :D), and if you let it go on long enough the electrolyte in the battery can boil off causing the battery to overheat and create a nice car-b-que.
Before it happened to my RSX I had no idea how dangerous it could be and what damage it can cause. My car's ECU had reset itself while driving... twice actually! :D I had a local mechanic look at the car but they couldn't find the cause. Yes in retrospect the mechanic was incompetent, but that's another story. :D It wasn't until I started hearing a whine from the alternator that I knew what was going on. I visited another mechanic and he literally told me to go buy a lottery ticket because as he put it, I had a lucky horse shoe up my ass. :D My battery was already boiling, and as he told me, he's seen it before where it's caused a car fire.
I then had a new battery and alternator installed. When I picked up the car and drove to work, on the way there I nearly seized the motor. I was stuck in stop and go traffic and I happened to look down at the temp gauge and it was pegged into the red zone. Long story short; the bad alternator completely fried one cooling fan and roasted the other one by about 90%. Just to get by until the part came in I had to run a jumper wire from the battery to the lone working fan and I had to crank the heat.
Oh, did I mention this was in the middle of a heat wave? :D It was in the middle of a heat wave BTW. :D
Between the alternator, battery, the cooling fans, and the labor costs, that $.50 diode that blew in the alternator caused $2000 worth of damage to my car. I'm convinced the only reason the engine didn't seize was because I was using Mobil1 in it. Thankfully I caught the boiling battery before it did even more damage than that.
In regards to our trucks though, I remember someone posting something about how they experienced similar ECU resets on their brand new truck and that their truck caught fire. I'll have to see if I can find the post about it but I wouldn't put it past it being caused by the above.